Mineral oil composition



Patented Feb. 17, 1953 MINER-AL OIL COMPOSITION Edward S. Blake,'Medford, Mass, assi'gnor to Monsanto Chemical Company, St. Louis, Mo.,a corporation of Delaware No Drawing. Application November 21, 1947,Serial No. 787,485

4 Claims. (01. 25246.6)

This invention relates to lubricating compositions and to methods ofpreparing the same and more particularly to lubricating compositionsadapted for use under extreme pressure conditions.

Various types of modern machinery such as the hypoid gears in motorvehicles develop enormous pressures'between engaged surfaces. Theordinary type of hydrocarbon lubricant composed only of a petroleumfraction is incapable of satisfying the severe requirements demanded inthe proper lubricant of hypoid gears, bearing surfaces, metal cuttingtools, and the like subjected to unusually heavy loads per unit area ofsurface. This invention has to do with ingredients which may be added toa suitable carrying agent such as mineral oil and are capable ofmaintaining between the engaged surfaces a lubricatin film under highpressures.

A primary object of this invention is to provide a new and novel sulfurbearing material capable of imparting desirable properties to alubricating oil composition otherwise unsatisfactory under theconditions encountered. A further object is to provide a mineral oiladjuvant which is not corrosive and does not decrease the oxidationstability of the oil. A still further object is to provide a class oflubricants capable of maintaining a lubricating film between surfacesengaged under high pressures. A still further object is to provide aclass of lubricants which reduce wear. hereinafter.

"In accordance with the present invention it has been discovered thatdi-esters of dihydric alcohols and unsaturated fatty acids can bereadily sulfurized to 'produce sulfurized diesters having valuableproperties which render them valuable as ingredients in mineral oillubricants. In general, the compositions of this invention compriseamajor proportion of mineral lubricating oil and a minor proportion ofthe sulfurized ester, as for example 0.1% to 30%. Other ingredients maybe present as desired, it being particularly advantageous to have aphosphorus ingredient present. Apparently phosphorus exerts a.synergistic effect on the sulfurized neutral esters since the wearresisting properties are greater than would be predicted from theproperties of the separate components. Phosphorus may be introduced byreacting the sulfurized ester with a suitable phosphorus component ashereinafter described or added as a separate component. Examples ofsuitable phosphorus compounds are mono oleyl phosphate, dioleylphosphate, mono lauryl phosphate, di lauryl phosphate, mono cresylphosphate, di cresyl phosphate, di cetyl phosphataand di octylphosphate.

Other objects will be disclosed The presence of a small amount ofanorganic halogen bearing compound is also desirable in the compounding ofsome types of lubricants.

The esters to be sulfurized are prepared by esterifying dihydricalcohols of the type where R is an alkylene group which may contain oneor more sulfur or oxygen atoms in the chain. Typical examples arealcohols possessing the formula HOC2I-l4OI-I, HOC2H4SC2H4OH,OHC2H4OC2H4OH, HOC2H4OC2H4OC2H4OH and the like. The alcohols areesterified with long chain unsaturated fatty acids,,as for example oleicacid, elaidic acid, erucic acid, linoleicacid, and ricinoleic acid.

The di-esters may be sulfurized in any suitable manner, the sulfurizedproducts being readily soluble and miscible with mineral oil fractions.Sulfurization may be effected by heating the ester with sulfur or amixture of sulfur and a sulfur halide at 150-200 C. Where the materialis then phosphorized, it is preferred to carry out the reaction undermilder conditions, say -125 C. The phosphoru sulfides, as for examplephosphorus pentasulfide or sesquisulfide are satisfactory phosphorizingagents. The following example demonstrates the sulfurization andphosphorization of glycol di-oleate and. is not limitative of theinvention.

EXAMPLE I Into a container of suitable capacity there was charged 2268parts by weight of glycol di-oleate and 193 parts by weight of sulfur.The mixture was heated for 7 hours at 177-183 C under an atmosphere ofnitrogen. 13 parts by Weight of phosphorus sesquisulfide was then addedand heating continued for 9 hours at -110 C. The product contained 8.02%sulfur, 0.29 phosphorus and had a neutralization number of 7.12. Theeffectiveness of the sulfurizedandphosphorized glycol di-esters may bedemonstrated by the conventional tests on compositionscomprised of theseingredients and a lubricating oil carrying agent. 'More specifically,aminor amount of the product described, in Example I was addedl'to ahigh viscosity hydrocarbon lubricating oil (Saybolt Universal viscosityof 101 secondsgat 210 F.) and samples of the blended lubricant subjectedto the Almen pin test described'in a paper presented before the. 13thAnnual Meetingof the American Petroleum Institute, Division ofRefilling, on November 17, 1932, by H. E. Wolf and H. C. Mougey-seeProc..A. P. I.. 1932, pages 118-430. In addition, the material wassubjected to the S. A. E. test described in the S. ,Al.. E. Jour- 3 nal39, 23-4 (1936). The results are summarized below:

Additionally, the aforedescribed sulfurized and phosphorized glycoldi-oleate passed the more important tests forming the basis of U. S.Army Specification 2-105B. Recognition by the Ordnance Department of theneed for a universal gear oil specification which wouldmore nearlydefine a satisfactory lubricant under field operating conditions in alltypes of automotiv gear drives, led through the efforts of theCoordinating Lubricants Research Committee to the formulation andadoption of U. S. Army Specification 2-105B.

-One of the important tests under this specification is that designatedby the Ordnance Department as AXS-1570 (C. R. C. Designation 1920-545).This test is a high torque low speed axle test and is described in theC. C. Handbook 1946, page 469.. A good pass was obtained with a solventrefined Mid-Continent oil containing of the sulfurized and .phosphorized4 weight of sulfur monochloride in 25 parts by weight of mineral oil (S.A. E. 10) and 37 parts by weight of sulfur. The air in the container wareplaced by hydrogen sulfide and the mixture heated with stirring for 7hours at l69-l71 C. .4 parts by weight of P483 was then added andheating continued for 5 hours at 104109 C. in an atmosphere of hydrogensulfide. The product contained 8.59% sulfur, 0.40% phosphorus and had aneutralization number of 4.85.

,A series of preparations were carried out in which glycol di-oleate wassulfurized by heating with sulfur in the ratio of parts of sulfur to 436parts by weight of glycol di-oleate. For the most part the reactionswere carried out either undernitrogen or hydrogen sulfide exceptExamples 4 and 1 0 which were preparedin ,air. No significantdifferences have been observed due to the presence or absence of aninert atmosphere. However, since hydrogen sulfide is evolved in thereaction, there may have been an effective atmosphere of hydrogensulfide in every case. Phosphorus sesquisulfide was then added and thecomposition heated'to effect phosphorization. The-table belowillustrates a variety of conditions and ratios under which the reactionsmay be successfully carried out. In Example 7 there was presentinaddition to the sulfur a small amount of a solution of sulfur chloride'in mineral oil. 3 parts orszcn dissolved in 25 parts of mineral oilwas. used for 436 parts of glycol di-oleate.

Example 4 5 6 7 8 0 l0 11 Time of sulfurizatiou, hours 7, 5 7.5 7. 5 1818" '7. 5 7. 5 7. 5 Approximate average temperature of sulfurization, Ov 170 170 -170 .170 170 180 180 180 Pisa, parts by weight 3 4- 8 '2 4 23 4 Timeofphosphorization, hours 5. 5 a 5 5 5 5- 5. 5 5 5 Approximateaverage temperature of phcsphorization, C.. 107 107 107 107 107 107 107107 glycol di-oleate. The composition also passed the high speed axletest designated by the Ordnance Department as AXS-1569 (C. R. C.Designation 'Ll9 -645) described page 467 of the c. R. c. Handbook 1946.Thus, the'preferred: additives have been found to bee'ntirelysatisfactory under conditions simulating actual Working conditions. Inorder further to demonstrate the invention, as-lar e umber f suliuri edand phosphoriz d t ve re pr pared der di e en cor uticns and tested ascomponents of mineral oil lubricating, compositions. Again, the examples:areito be taken as illustrative of the invention and not limitati-vethereof.

' EXAMPLE 2 Into av glassor glass lined reactor of suitable .capacitythere wascharged 436 part by weight of glycol di-oleate, 2.5 parts byweight of sulfur ingnochloride dissolved in 25 parts by weight ofmineral oil (8. A. E. 10) and 3'7 parts by weight Analysis gave 7.03%sulfur, 0.27% phosphorus and a neutralization number of 2.4.

7 EXAMPLE 3 {Into a glass or glass lined reactor of suitable capacitythere was charged 436 parts byweight of-*glycol di-oleate, a solution of2.5 parts by Analysisof the compositions of Examples 2-11 gave anaverage sulfur content of 6.8% and phosphorus ranging from 0.22% in thecase of- Ex-. ample 7 to 0.6% depending upon the amount charged. Theneutralization number varied from 5.6 to 13.6. These compositions wereevaluated as components of gear lubricants under-high torque and lowspeed conditions by an adaptation of the S. A, E. extreme pressurelubricant testing machine. p I The machine employed for the test was anS. A. E. extreme pressure lubricant testingmachine manufactured bytheHighway Trailer Co., Edgerton, Wisconsin. This machine, suitablymodified, provides. a simpl convenient means of imitating the rubbing ofgear teeth by rotating two Timken test cups in line contact with eachother and in opposite directions, undercontrolled rotation speeds. Forthese tests the speed of the main shaft was reduced from 1000 to 264 R.P. M. and the lower shaft drive gears of 20 and 81 teeth replacedwith'gears of 52 and 49 teeth to change the rubbing ratio from 14.611 to'over the test cups to prevent direct heating of the cups.

Test procedure Two Timken test cups are weighed to the nearest milligramand fastened in place on their respective shafts. the carriage withknife edges in place; the thermocouple junction is adjusted to onequarter of an inch below the lower cup; the plate holding the oil sealis tightened; the coupling links are inserted on the upper and lowershafts and the oil box locked into position.

A twenty pound scale load is applied by hand and the cup alignmentchecked for perfect contacting edges and adjusted if necessary. Thetwenty pound load is released and the water lines are connected.

The oil is to be tested is then added until the lower test cup is halfimmersed. This oil level is maintained for the duration of the run byadding more oil when'necessary. The oil box bearings are lubricated withthe oil to be tested.

With the temperature recorder-regulator in operation, the machine isstarted and the load is taken up to fifty pounds, where it is maintainedfor a break-in run of one-half hour. the end of the break-in the load isbrought up The oil box is positioned in to 110 pounds by the automaticloading device face disturbance than does'the top ring, a phe-';

nomenon for which there are several theoretical explanations.

The inspection terminology used in describing the ring surface isessentially that given in the C. R. C. Designation 1,-20-545, namely:(a) burnish, (b) smoothing, (c) rippling, (d) ridging, (e) pitting and(f) galling. Burnish is an alteration from the original ground dullsurface to a brightly polished surface and is usually accompanied bysome alteration in or elimination of the grinding marks. Smoothing isthe elimination or near elimination of the grinding marks where thesurface finish usually remains dull. surface patterns, dull or shiny,resembling fish scales or ripples on water. Ridging as here used is alongitudinal furrowing or channeling as a result of a wearing force.This is actually a misnomer as grooving would be a more accuratedescriptive term. Frequently rippling appears in the base of the grooveindicating this may have been the precursor 'of grooving or ridging.Pitting is the formation of small pit-like cavities. Galling isdifficult to describe but refers to a surface alteration which appearsto be a slight lengthening, widening, deepening and blackening ofindividual grinder marks. This may be due to localized chemical attack.

Rating 7 correlation. By a study of a backlog of samples .upon which theL-ZO results were known, a

basis for the overall appraisal of the test specimens was establishedpermitting a final classification as an L-20 pass or failure. A passingtest rarely shows a total weight loss of more than 20 mg. and no lightridging. A test rated fail usually shows a weight loss of appreciablymore than 20 mg. although it may in some cases be appreciably less.However, all of the described surface disturbance conditions may app-earand usually do in the more severe failures.

A tabulation of top and bottom test ring observations is shown in thetable below:

2 18 a }pass.

3 18 2 Do. 4 1s Do. 5 10 3 Do. 6 1s Do. 1 18 g Do. 8 1s Do. 9. 10 g Do.10 18 g Do. 11 is g Do. 11 10 g Do.

Inspection A series of preparations were carried out in Upon completionof the test, the test cups are cleaned and reweighed to the nearestmilligram for total weight loss, then inspected microscopically, oiledand filed for future reference. The rating, of the completed testdepends primarily uponthe visual inspection of the test cups. In

which glycol di-oleate was sulfurized by heating with sulfur in theratio of 37 parts by weight of sulfur to 436 parts by weight of glycoldioleate. Except, for Example 13, an atmosphere of hydrogen sulfide ornitrogen was employed. Phosphorus sesquisulfide was then added and mostinstances the'bottom ringshows more sur- 75 the mixture heated to effectphosphorization;

Rippling is the formation of transverse 8 The sulfur and phosphorusfigures :given in the above table are :in general :the average fromseveral Iidentical preparations. The neutralization number varied :from4.51: 16.6, the average being EXAMPLE J26 Sulfurization iand:phosphorization of diethyl- Example .Q. .I 12 is 14 is 'I-ime -ofsulphurization,hrs; 7 7 13.5 17.5

Aggroximate ave. temp. of sulphuriza'tion,

P483, parts by 'weight 2 4 2. 5 1

Time of phosphorization, hrs-. 5 5 5 Approximate ave. temp. ofphosphor-im i tion, C .107 107 107. 107

The sulfur content of Examples 12-21 aver-' aged about '7.6'%"andphosphorous ranged from 0.14% in Example 'to 0.47% in "Example 19.

The neutralization number varied from 3.7 to 10.6, the average being7.3. I

"Afsummary cf the modified S. A. E. test described above on .oils'containing these products is tabulated below ene glycol di-oleate wascarried out in at atmosphere of hydrogen sulfide. 436 parts by weight of'diethylene glycol di-oleate .was heated 7 hours at'169171 C. with 34.5parts by weight of sulfur. 6 parts by weight of phosphorus sesquisulfidewas then added and heating under hydrogen sulfide continued for 5 hoursat 104-110'9" C. The product was soluble in mineral oil and had'aneutraliza- Ewe O11 Additive, Percent a Final Ratin EXamPleNa l on onRing Rldgm Rippling I Lglsgs, t 12; 1'8 2 }pass. 13-. "18f Do.

, 4 borderline. 14 11 pass. 15 1s g Do.

is 1s Do.

16.. 10 Do. 17 10 "Do. 18 10' Do.

20 18 1g Do.

9i borderline. 17 }pass.

As still vfurther embodiments of the invention,

glycol di-oleate was sulfurized by heating with conditions of reactionare set forth in the following table. Examples '22 and 25 were preparedby heating in an atmosphere of hydrogen sulfide or nitrogen but noextraneous atmosphere was used in the case of Examples 23 and 24.

Example 22 23 24 25 Time of sullurization, hrs 7. 5 7. 5 7. 5 7. 5Approximate average temperature of suliurizatiou,'C 180 180 180 180 Psa, parts by weight... l 2 3 4 'limeof phcsphorization, hrs. 5 5 5 5Approximate average temperature of phosphorization, C 107 107 107 107Sulfur in final product, percent- 8.2 8. 3 8. 4 8.6 Phosphorus in finalproduct,

percent 0. 11 0. 23 0. 35 0. 46

tion number of 10.6. Analysis gave 0.80, 0.90% phosphorus and 8.02%sulfur.

EXAMPLE 2'7 Sulfurization and phosphorization of dithio diglycoldi-oleate was carried out in an atmosphere of nitrogen. 250 parts byweight of dithio diglycol di-oleate was heated with 14.9 parts by weightof sulfur for 7 hours at 178-182 C. 1.5 parts by weight of phosphorussesquisulfide was then added and heating under nitrogen continued for 5hours at 104-110 C. The product was diluted with petroleum ether,filtered through a bed of clay and the solvent removed by vacuumstripping u to C./3 mm. Anoil soluble product was obtained whichcontained 11.4% sulfur and 0.16% phosphorus.

The compositions of Examples 22-27 were added to mineral oil andsubjected to the .modie 55.5 parts by weight of sulfur under anatmosphere of nitrogen for 7 /2 hours at 181-186 C. In another typicalpreparation glycol di-oleate 35 *w'as sulfurized by heating 1275 partsby weight fled S. A. E. test described. The results are summarized belowI 1 Ring Ridging Rippling g Final Rating 22 18 3 }pass.

23 18 g Do.

24 1o Do.

25 1s Do.

I some pittin l2 borderline. 18 light 13 }pass.

27 1o ,3 Do.

It is evident from the foregoing examples that glycol di-esters ofunsaturated fatty acids may addition, the esters may be reacted withsulfurizing and phosphorizin agents in difierent ratios than thosespecifically mentioned. Obviously,

sulfurized esters may be produced by elimination 30 of the phosphorizingstep. For example, 654 parts by weight of glycol di-oleate was heatedwith of the ester and 96 parts by weight of sulfur for 8 hours at181-184 C. The reaction product was then heated with approximately 5% byweight of Attapulgus clay at 100 C. and filtered. Other Composition A:Oil+6.0% product of Example 28.

2.0% chlorinated kerosene (58-67% Cl), 0.5% mixture of monoand di-laurylphosphate.

Composition B: Oil+ 10.0% product of Example 29.

2.0% chlorinated paraffin wax (40% Cl) 0.4% mixture of monoand di-laurylphosphate. r

Composition C:

, Oil+6.0% product of Example 30.

2.0% chlorinated kerosene (58-61% Cl). 0.5% mixture of monoanddi-oleyl'phosphate.

These compositions were subjected to the modified S. A. E. test todetermine their wear resisting properties. The results are summarizedbelow:

Wt. Composition Ring Ridging Rippling Ifioss Final Rating p 0 0 2 Abottom 0 0 9 Pass. B tqp. incipient trace 1 borderline.

""""""""""" bo 2 0 8 pass.

O {bo f m n 0 2 Do.

sulfurizations were carried out in similar manner. The glycol .di-oleatewas heated with sulfur at a temperature within the range of 180-188 C.for

' 7 hours, then heated with Attapulgus clay and i'filtered'through alayer of diatomaceous silica.

The series of preparations is summarized in the following table in whichthe sulfur is expressed as parts by. weight per 436 parts by weight of60 glycol di-oleate. i

. Example 28 29 30.

Sulfur 32. 8 37 42. 7 Percent Sulfur in product 6. 11 7. 68 8. 2

Copper strip tests showed that the sulfurized products were notcorrosive to copper. The tests were conducted by immersing a cleanbright cop- 7 per strip in mineral oil containing 5% of the sulfurizedester and heating 1 hour at 150 C. In addition, S. A. E. grade gear oillubricant compositions were compounded from a Mid-Continent solventrefine oil as follows: 7

In addition to gear lubricants, other types of compositions may becompounded from the new adjuvants, as for example crankcase lubricants,spindle oils, turbine oils, insulating andtransformer oils, slushingcompositions, greases,etc. Effective non corrosive cutting oils havebeen prepared. For instance, the addition of either of 5% or 10% ofsulfurized and phosphorized glycol di-oleate to a paraflin oil providedcompositions exhibiting high Oster threading .efiiciency and hightapping efiiciency. Copper be prepared by heating the base with l-12%sulfur and then with 02-20% phosphorus sesquisulfide. In some instances.substantially neutral products have been prepared but. for themost partthey exhibit a mildly acid reaction. So far 5 as is known, this is not acritical feature since all of the products proved to. be substantially,equivalent over the range stated. Products having neutralization numbersup to 18.6 have. been. examined.

The conditions of carrying out the reaction are. also subject tovariation. However, in general no advantage is obtained by conductingthe sulfurization at higher temperatures: or for longer times than thoseillustrated above In fact, the 15..

products are then generally less satisfactory'and contain less sulfurthan products. preparedunder milder conditions. Lower temperatures maybeemployed where desired in which case it is advantageous to employ asulfurization catalyst in order to secure a rapid rate of reaction.Small amounts of acidic materials, as for example toluene sulfonic acid,sulfuric acid, phosphoric acid and the like may be employed to catalyzethe sulfurization.

Although thepreparation of the phosphorized esters. by' means ofphosphorus. sesquisulfide has .been described in specific examples; it.will be properties and may be employed in conjunction with othert-ypesofadditives which would. otherwise be corrosive; They are compatiblewith mineral oil fractions in high proportions and.- with most othertypes of materials employed in the 40 compounding of mineral oillubricants. They may be used in conjunction with such products aschloronaphtha ethyl xanthate, di-trichlorohenzyltrithiocarbonate.di(ethylene glycol mono.

oleate) malate, and other esters, halogen bear:- ing esters, halogenatedhydrocarbons,phosphorusbearing esters and thelike'. In. addition, theadditivesv maybe supplied in the form'of' concenI-- trates or in otherwords, mixtures of lubricating oil and of additives in which theadditives are present in amounts appreciably higher than thoseultimately'appearing in the mineral oil lubricant, as for example 75'parts-of sulfurized ester and 25 parts of mineral oil.

The present invention is limited: only by the claims attached heretoaspart of the present specification.

What'is claimed is:

1'. A composition'of matter useful as a lubricant consisting essentiallyof a major amount of mineral oilthelubricating properties of which areenhancedin-the respect that the-Wearing of lubricated metal surfacesisreducedby'havi'ngincorporated therein in amount effective toreducewear an additive composition containing 5.8%-11.4% sulfur and0.11%-0.80% phosphorus. suppliedessentially by a sulfurized andphosphorized ester ofthe-group'consisting of ethylene glycol dioleate,diethylene. glycol dioleate and dithio diglycol dioleate obtained by"heating with sulfur at 150- 200 C. and phosphorizing at IOU-125 C.

2. A composition of matter useful as a lubricant consisting essentiallyof a major amount of mineral oil the lubricating properties of whichare-enhancedin the respect that the wearing of lubricated metalsurfacesis reducedby having incorporated therein 5%1-18% based on the oil ofasulfurized and phosphorized di-oleate of a dihydric glycol selected"from the group consisting of ethyleneg-lycol, diethylene glycol anddithio diglycol containing 5.8 %-11.4% sulfur and 0.11%- 0;80%,phosphorus obtained by sulfurizi'ng'at 150- 200"C. and phosphorizing atIOW -125 C.

3'. A composition of matter useful as a lubricant consistingessentially-- of a major amount of mineral oil the lubricatingproperties of which are enhanced in therespect that the wearing oflubricated metal surfaces is reduced by having incorporated therein5%-18% based on the oilof sulfurized' and phosphorized ethylene glycoldioleate containing: 5.8%'-8.6% sulfur and 0.11%- 0280 phosphorusobtained by sulfurizing' at 150- 200 C. and phosphorizi'ng at 100425 C.

4} A composition of matter useful as a. lubricant consisting essentially"of at major amount of mineral oil the lubricatingproperties of whichare enhanced in the. respect that the wearing. of lubricated; metalsurfaces. is reduced by having incorporated" therein at least: 0.1by'weight based upon the mineraloil' of a: sulfurized and phosphorized:ethylene. glycol di-olea-te: containing 5.8%11.4% sulfur and 0.11%-0.80% phosphorus obtained by heating the ester with sulfur at 150-20.0. C. and with aphosphorus sulfide at C.

EDWARD S. BLAKE.

REFERENCES CITED The following references are of record in the file of'this patentz.

UNITED STATES PATENTS Number Name Date 2,179,067- Smith Nov. '7, 19392186;646 Lincoln et'al. Jan. 9, 19.40 2,211,231 Henderson Aug; 13,194023211306- Whittier Aug. 13, 1940 2,225,365 Bray Dec. 17, 19.40 2,415,838Musselman et al; Feb..18, 19.47 2,422,630 Musselman et a1. .June 17,1947$441,587 Musselman May 18, 1948 2,483,600 Stucker Oct. 4, 1949 2,541,789Stucker Feb. 13, 1951 2 ,542,161 Stucker ..Eeb. 20, 1951

1. A COMPOSITION OF MATTER USEFUL AS A LUBRICANT CONSISTING ESSENTIALLYOF A MAJOR AMOUNT OF MINERAL OIL THE LUBRICATING PROPERTIES OF WHICH AREENHANCED IN THE RESPECT THAT THE WEARING OF LUBRICATED METAL SURFACES ISREDUCED BY HAVING INCORPORATED THEREIN IN AN AMOUNT EFFECTIVE TO REDUCEWEAR AND ADDITIVE COMPOSITION CONTAINING 5.8%-11.4% SULFUR AND0.11%-0.80% PHOSPHORUS SUPPLIED ESSENTIALLY BY A SULFURIZED ANDPHOSPHORIZED ESTER OF THE GROUP CONSISTING OF ETHYLENE GLYCOL DIOLEATE,DIETHYLENE GLYCOL DIOLEATE AND DITHIO DIGLYCOL DIOLEATE OBTAINED BYHEATING WITH SULFUR AT 150200* C. AND PHOSPHORIZING AT 100-125* C.